1. Field of the Invention
The present invention relates to recording sheet usage count evaluation method and apparatus for evaluating a cumulative usage count of each recording sheet (also called “imaging plate”) in a radiation imaging system, in which a radiographic image is recorded on the recording sheet by imaging an object by using a radiation imaging apparatus, image data is obtained by reading the radiographic image recorded on the recording sheet by using a radiographic image reading apparatus, and the image data is processed by using a medical image processing apparatus. Further, the present invention relates to a medical image processing apparatus using such a recording sheet usage count evaluation method.
2. Description of a Related Art
Conventionally, an imaging method using a radiation (X-ray, α-ray, β-ray, γ-ray, electron beam, ultraviolet ray, or the like) is utilized in various fields, and particularly, employed as one of the most important means for diagnosis in a medical field. Since a first X-ray photograph was realized, X-ray photography has been repeatedly improved, and presently, a method using a combination of a fluorescent screen and an X-ray film is going mainstream. On the other hand, in recent years, various digitized apparatuses such as X-ray CT apparatus, ultrasonic apparatus or MRI apparatus are in practical use, and construction of diagnosis information processing systems in hospitals is being developed. As for X-ray images also, many studies have been made for digitization, and a radiation imaging method using a photostimulable phosphor has been established, which attracts many attentions as a method that will replace conventional X-ray photography.
The photostimulable phosphor (storage phosphor) is a substance in which a portion of radiation energy is stored when the radiation is irradiated thereon, and thereafter, stimulated fluorescence is emitted according to the stored energy when excitation light such as visible light is irradiated thereon. The existence of the photostimulable phosphor has conventionally been known. The radiation imaging method using the photostimulable phosphor will be described below. First, by using a radiation imaging apparatus, a radiographic image of an object such as a human body is taken on a recording sheet (imaging plate), onto which photostimulable phosphor is applied, and recorded thereon. Then, by using a radiographic image reading apparatus, the recording sheet is scanned with excitation light such as a laser beam, and thereby, stimulated fluorescent light is read out photoelectrically to obtain image data. Further, by using a medical image processing apparatus, after the image data is properly processed, the radiographic image is output on a display such as a CRT, or printed out on a film by using a laser printer, etc., and thus, the radiographic image can be displayed as a visual image.
Such a radiation imaging method has a performance comparable to the conventional X-ray photography in terms of imaging sensitivity and image quality. For example, as compared to the conventional X-ray photography, the exposure range is extremely large, and the response of the stimulated fluorescent light to the light exposure is substantially proportional throughout the whole exposure range. Accordingly, when the object is imaged under any radiation dose, it is possible to capture the luminescent range of the image existent therein, and obtain a digitized signal through normalization without shortage or excess. Also, by combining the obtained signal with a proper image processing method, it is possible to constantly provide an image of excellent quality under a variety of imaging conditions. Further, because of direct acquisition of digitized image information, not only long-term preservation of a large amount of data without deterioration, but also development for use in a medical diagnosis information system becomes possible.
Now, generally, the recording sheet is contained into a case, called “cassette”, when in use. As an identification mark for distinguishing a recording sheet for imaging one patient from a recording sheet for imaging another patient, a barcode is attached to the recording sheet, which can be viewed through a window provided on the cassette.
When the recording sheet contained in the cassette is repeatedly used for radiation imaging and radiographic image reading, the characteristic thereof is degraded because of bending in the radiographic image reading apparatus or secular change, which tends to bring about deterioration of the image quality. In order to estimate such image quality deterioration beforehand, it is desired to confirm a cumulative usage count of each recording sheet.
However, in general, the recording sheet is neither specified for each radiation imaging apparatus nor specified for each radiographic image reading apparatus, but commonly used for a plurality of radiation imaging apparatuses or a plurality of radiographic image reading apparatuses. Therefore, it has not been realized to confirm the cumulative usage count of each recording sheet. Further, the degree of degradation in the characteristic of the recording sheet varies with difference in type of the radiographic image reading apparatuses, difference in installation environment of the radiographic image reading apparatuses and difference in manufactured time of the recording sheets, and therefore, it is desired to confirm the usage state of the recording sheet, taking into account at least one of the above factors.
As a related art, Japanese Patent Application Publication JP-P2001-154297A discloses, in an image information record reading apparatus of a built-in type, to efficiently perform confirmation of the necessity for cleaning and exchange of sheets. In the image information record reading apparatus, there are provided counter means for counting the frequency of feeding a sheet (IP: imaging plate), a display panel for indicating a counted count value, and a buzzer for generating a warning beep depending on a predetermined frequency when the count value reaches the predetermined frequency. By using the count value indicated on the display panel or the warning beep generated by the buzzer, a user can decide the necessity of cleaning or exchange of the sheet (IP).
However, the art disclosed in the above JP-P2001-154297A is limited to an image information record reading apparatus of a build-in type, and it is not possible to apply to a general system in which a recording sheet is commonly used to a plurality of radiation imaging apparatuses or a plurality of radiographic image reading apparatuses.
Further, Japanese Patent Application Publication JP-P2003-220054A discloses, in a medical image reading system, to achieve a reduced maintenance work as well as a reduced cost, to enable prompt handling at the time of the occurrence of an error, and to maintain each apparatus constituting the medical image reading system to an optimal state. In the device information collection processing of the above system, a control section in a controller stores error information in regard to the controller, a reservation device and a reading device into an error log information table for each apparatus, adds up an error occurrence frequency for each error item, and makes an error log information indication screen to be displayed on a display section.
However, the medical image reading system as shown in FIG. 1 of JP-P2003-220054A includes only one reading apparatus (radiographic image reading apparatus), and no suggestion is made in regard to application to a general system in which a photostimulable phosphor plate (recording sheet) is commonly used for a plurality of radiation imaging apparatuses or a plurality of radiographic image reading apparatuses.